Inclined gyro vertical



Sept. 2, 1952 H. H. THOMPSON INCLINED GYRO VERTICAL Filed Sept. 26, 1946 INVENTOR HERBERT h. 72/044, 30 35 flaw M H [5 ATTbRNEY Patented Sept. 2, 1952 Herman; Thompson, Manhasse N, mam

91 Sperry Corporation, a corporation oif Delaware Application September 26, 1946', Serial'No.-699,5 72

In Great-Britain March-13,1946

This invention relatesrto gyro-verticals: r gyroscopic artificial horizons designed;- for; use. 1 moving craft such as ships. or aircraft's. A 1 scribed in the prior patent o-fFrederi-ck Damagidon, reissued as No; 23, 291 iorGy iO-verwpl originally filed April 16, 11941:, and in the joint application of'Frederick D. .Braddonand Walter Wrigley, Serial No. 566,568 :for Inclined Gyroscopic Horizons. filed December 4, 194A, t i now known that turn errors in the ordinary gyro-vertical whichv is. erected by. a torqueapplied about a horizontal axis. at right, angles .10 the relative tilt of the. gyroscope, and gravitational controller may: be largely mitigated by forwardly inclining the "gyroscope at a correct angle. Such a correction, however, asheretoiore proposed was only partial. If the aioresaid gravitational erection device applies a torque which is substantially constant, regardless of rate of turn or speed of the craft, such correction is only exactly correct for a predetermined rate of turn of the craft as particularly pointed out in the aforesaid Braddon sole application. If, however, the gravitational erection device applies a torque which is substantially propor tional to the lateral acceleration force due. to turns or, in otherwords, proportional to the tangent of the relative. tilt angle of the gyros and a free pendulum (which is the bank angle of the craft) such correction is only complete if, when the turn takes place, the airplane is. flying at the predetermined air speed for which th instrument is designed.

Also, in the aforesaid solutions, while the error due to turn is substantially curedundercertain predetermined conditions and greatly miti ated under conditions which vary thereiromin the particulars pointed out above; no. correction; is secured in these prior devices for changes speed of the craft. In other words, upon. chan e of speed of the craft, the gravitational responsive controllers cause a temporary deviation of the gyro-vertical, which shows up usually. after the aircraft has arrived at its'new spent. and persists until corrected by the erection device.

My invention is. mainly concerned with the type of erection device which gives a torque proportional to the lateral acceleration force. By my invention, I not only furnish a complete. cure for turn errors at all ordinary airspeeds and rates of turn, but also prevent theoccurrerice of errors due to change oflinear speed of the craft j 6, Claims. (01.. 74 -.-5 .47

and I; accomplish. bothv of; these. results. hit-- one and the. same means and in. one and t ersame operation; I 1 C d n to.- my invent on, so de my inclined gyro-vertical and so; arrange the various factors. thereof, namely, the angle inc at o he'er ction torque radient TQK), that isy'the ratio of the, erectin torque to cl natio the mome t; of inertia. of the r to M and the rotor speed (m), that no turn error is apparent regardless of the rate of turn when the craft is flying at its. normal. or cruising speed. As explained above, this involves the use of a proportional torque applying device, instead .o the on-off type device first described above, since in the former the amount of the error due to turns is substantially unaffected by the rate of turn and only affected by linear speed during the turn.

According to my invention, I propose to employ a single gyro rotor with a forward-inclina: tion a, and to vary the rotor speed (w) thereof with changes of speed of the craft leaving the angle of inclination constant. By this means a proper rate of precession of the inclined axis is in azimuth maintained for all air speeds since, while a change of air speed does change the lateral acceleration iorcehcting on the bank pendulums during aturn, this is compensated for by the fact that the rotor speed is also changed proportionally to air speed so that the angle of inclination may remain constant.

It may also be shown mathematically and experimentally that the change of speed error due to the effect of acceleration on the pitch pendulums is also cured by changing the rotor speed simultaneously with and proportional to the chan e or sp ed.- .In o her w rds. he reaction on the: yroscope h in se tle en m he fore-and-.%ft axis a c ler t n e de l rating the r, ap lies a. or su fi iea t9 QPP -i and prevent an QSCillhIiQR b ill HR 2 pitch erection device'due to the Ht E QB 9.? 2h? 52* celeration forces thereon at the time.

To restate the foregoingmathematically:

(l) The basic law'governing the remoyal of the turn errorin this type of gyrorvertical may be simply stated as follows:

where a=the angle of inclination of the gyro,

K =the erecting torque gradient, that is, the ratio of the erecting torque to inclination,

.S'=the speed of the craft,

w=the rotor speed,

M =its moment of inertia, and

g=the acceleration of gravity.

While the foregoing shows that for curing the turn of error, maybe varied directly with S or (a) may be varied directly with S, or (K) may be varied inversely with S, I propose to vary (to) with S both because of simplicity in structure and because it also cures the errorsdue to the linear acceleration force during the change of speed of the craft as stated above.

The manner in which the effect of linear acceleration on the pendulums (i. e., acceleration due to speed changes) is compensated will be apparent from the following analysis. Assuming an increase in speed causing such an acceleration (dS/dt), the pitch pendulum which controls the-torquer leans backwards and causes a torque to be applied to the gyroscope in a direction to cause it to follow the tilt of the pendulum. Since the erection signal is proportional to (dS/dD/ it is required that'thehorizontal component (sine a) of the gyro momentum furnish an equal and-opposite torque. The follow- 'ing expression therefore-gives the conditions that need be met in order to compensate for straight line accelerations in the direction of flight,

By integration,

Mco sin t=K+a constant .(The constant is zero in the apparatus shown.)

or, a. being small,

KS Mwy This expression is identical with that for compensation of longitudinal accelerations and shows therefore that if (.0 is varied proportionally with S, the errors due toacceleration of the craft, whether the acceleration be dueto turns or changes of speed or both, are fully compensated.

The gyroscopic structure in all figures is shown as enclosed in a casing I mounted for freedom on the craft about a fore-and-aft trumiion axis 2 and a lateral gimbal axis 3. While the gyroscopic structure usually preferably comprises but a single gyroscope with its spin axis at a small angle (a) to the vertical; such structure may, of course, comprise a plurality of gyroscopes as both types of gyro-verticals are well known. (See Patent No. 1,236,993 to Sperry and Tanner.) The gimbal ring 4 is journalled in a long bearing 2' on said fore-and-aft axis and is open at the front or U-shaped to furnish an unobstructed view of the indicating portion of the instrument, which may be in the form of a spherical shell 5 (see also Fig. 2) enclosing the gyro casing on Referring to the drawings, several forms of my invention are disclosed as follows:

Fig. 1 is a diagrammatic perspective view of my improved inclined gyro-vertical; and

Fig. 2 is a side elevation, partly in section, showing my invention as applied to a similar gyro having somewhat a different type of erection device.

which suitable pitch and roll indicating lines 1 and 8 are placed. The gravitational control is shown as furnished by a pair of pendulums 9 and I0 pivoted respectively about fore-and-aft and transverse horizontal axes, each pendulum controlling a signal means responsive to relative inclination of the pendulum and gyroscope about: its pivotal taxis. Electrical pick-01f or signal generating means ll; 12 is shown in this figure for each"- pendulum. .Insteadof freely pivoting thependulums as is usually done, I prefer to pivotally connect them to the gyro casing by shortfairly stifi leaf springs 13, I4, so as to greatly restrain their outward movement during a change of speed or during turns and to cause such movementto be substantially proportional to the amount of such lateral acceleration force, which is proportional to the tangent of the angle of tilt between the gyro and the affected pendulum. Such a. suspension causes the pendulums, to act more as accelerometers than pendulums, although still responsive to gravity, since in this structure, the displacement of the pendulums from normal remains substantially proportional to the banking angle even during high rates of turn at high speed, since the springs are made stifi" enough to prevent the pendulums from' swinging beyond the control range of the signal transformer pick-offs ll, l2 provided in connection therewith. The windings on said pick-offs are omitted in the drawings for simplicity.

Each of these pick-ofis is shown as of the E" or three-legged type mounted directly under each pendulum and giving an A. C. output proportional to the amount'o'f relative displacement of the pendulum and the gyroscope from norm, and reversible in phase with the direction of displacement. The output of the transformer l I, after passing through phase-sensitive amplifier i5, is applied to a suitable torque applying motor l6, acting about the transverse axis 3 to apply a torque on the gyroscopeat right angles of the tilt and proportional to the lateral acceleration force. Similarly.'the transformer l2.under the spring-restrained pendulum It) applies through amplifier l5 a proportional torque about the fore-and-aft axis to the gyroscope through the torquer l6. v

The tilt angle (a) is maintained in Fig. 1 by connecting the pendulum structure to the gyro at an angle, so that when the fore-and-aft swinging pendulum I0 is hanging vertically, the vertical axis of the gyro unit is inclined forwardly at the predetermined-angle (a); It is obvious that the same result'may be secured by mounting the pendulum structures symmetrically on the gyro and by biasing the pendulum to 7 hang at the required inclination, as shown in 24 is provided within the container around shaft 25 to hold the diaphragm in a midposition while the aircraft is flying at normal or cruising speed. While the movements of the diaphragm 2| may be transmitted directly from shaft 25 to a rotor speed governing device, I prefer to interpose a correction device which corrects the indicated air speed which would be given by the output or movements of the shaft 25, so that a movement is obtained which is indicative of true air speed, since the rotor speed should be corrected for true air speed rather than an indicated air speed.

The drawings are intended to represent diagrammatically one form of known true air speed meter such as is more fully described in the patent to Spencer Kellogg, 2nd, No. 2,496,294, dated February 7, 1950 for Speed Governing System for Dirigible Craft. For this purpose shaft 25 is shown as governing the position of a slider 26 on resistance or potentiometer 21 which is in series with a shunt field 28 of the motor 29 which spins the gyro rotor, but the position of slider 25 is also corrected by sealed bellows 30, connected into the linkage 3| connecting shaft 25 and arm 26. Link 3| of this linkage is also made temperature sensitive, so that temperature and air density changes are compensated for. When the aircraft is going at a maximum speed, the slider introduces the maximum resistance 21 into the field circuit so that the rotor at that time is driven at its maximum speed. For lesser speeds, the resistance is cut-out until the field strength is a maximum and the motor is driven at its minimum speed, which is usually taken to be about the stall speed of the craft. Hence, the main starting switch of the motor 29 may be closed while the aircraft is still on the ground so that the rotor will be brought up to this minimum speed.

Preferably, however, I provide a bridge circuit 32 around the potentiometer arm 26 which circuit may be closed by operating a switch 33. This circuit is connected to a midpoint on a potentiometer so that when the switch is closed, the rotor is spun at a speed which preferably corresponds to the average or cruising speed of the craft. Preferably, the instrument is so designed that the forward inclination a is such that the turn error is completely cured when the airplane is flying at cruising speed, with the speed of the rotor about midway between its maximum and minimum speeds. Therefore, the switch 33 may be used to advantage in testing instruments under average flight conditions.

In Fig. 2, I have shown my invention as applied to a gyroscope having a slightly different form of erection device but which gives a torque proportional to tilt through a substantial angle although through a lesser angle than in Fig. 1. This erection device is of the eddy current type and is shown and described more particularly in the prior patent to Frische and Esval, No. 2,229,645, dated January 28, 1941 for Electro- Magnetic Erection Devices for Gyroscopes. Ac-

member 36 is so pivoted, said ring 31 being journalled in the instrument by means of a long sleeve 38 and suitable bearings 39. The gimbal ring 4 is in turn journalled in sleeve 38 by bearings do and in this form sleeve 38 constitutes the main longitudinal bearing for the gimbal ring 4. The variation of the rotor speed may be accomplished in the same manner shown in Fig. 1 from a true air speed meter (not shown).

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A gyro-vertical for dirigible craft in which the gyro unit is forwardly inclined for eliminating turn errors, means responsive to the air speed of the craft, and means for varying the rotor speed thereof proportionally to variations in the response of said first means with air speed changes.

2. A forwardly inclined gyro vertical as claimed in claim 1 in which said air speed responsive means is compensated for temperature changes so as to be responsive to true air speed.

3. A gyro-vertical for dirigible craft having a gravitationally controlled power erection device of the proportional type so constructed and arranged as to cause the gyro to remain forwardly inclined at a constant angle to reduce turn errors, means responsive to the air speed of the craft, and means for varying the rotor speed with changes of said speed responsive to said first means to eliminate all acceleration errors whether linear or centrifugal.

4. A gyro-vertical for dirigible craft in which the gyro unit is forwardly inclined for eliminating turn errors, means for spinning the rotor, means for progressively varying the speed at which said rotor is driven, a true air speed measuring device, and means for operating said speed varying means from said device, whereby all acceleration errors are substantially eliminated.

5. A gyro-vertical for dirigible craft in which the gyroscope is forwardly inclined about one of its gimbal axes for eliminating turn errors, a gravitational controller acting about each of its gimbal axes having an output proportional to acceleration forces having a horizontal component affecting the respective controllers, a torque applying device about each of said axes of the gyroscope controlled respectively by one of said controllers and means for varying the speed of the rotor of said gyroscope proportional to the speed of the craft.

6. In a gyro-vertical for dirigible craft of the single gyro type in which the spin axis of the gyro is forwardly inclined for reducing turn errors, spinning means for the rotor of said gyro, means for selectively varyingthe speed at which said rotor is spun, an air speed measuring device, and means for operating said speed varying means from said device to maintain a rotor speed proportional to air speed, whereby both turn and acceleration errors are reduced.

HERBERT H, THOMPSON.

REFERENCES CITED The following references are'of record in the file of this patent:

Number 8 UNITED STATES PATENTS Name Date Gray Jan. 23, 1923 Ford May 10, 1927 Glitscher Oct. 24, 1933 Gillmor Jan. 8, 1935 Meredith Jan. 2, 1945 Braddon Oct. 22, 1946 Haskins, Jr. et a1. Dec. 17, 1946 Schoeppel June 28, 1949 

